This invention is particularly useful in, but not restricted to, a thermal printer such as described in U.S. patent application Ser. No. 457,593, filed Dec. 27, 1990 in the names of S. Sarraf, et. al., and having a common assignee with the present patent application. This printer thermally prints an image on a receiver element, which may be in the form of a slide transparency, by scanning a laser beam across a dye-donor element held against the receiver element (e.g., slide transparency). The laser beam is modulated by input data corresponding to the image to be printed. The modulated beam, which is focused to a small spot, is swept across the donor element a line at a time by an electromechanical galvanometer which rotates a mirror to deflect the laser beam linearly. Thermal energy from the focused spot of the laser beam causes small dots or pixels of dye from the donor element to thermally react and to transfer pixel-by-pixel to the receiver element. A finely detailed image is thus printed on the receiver element by the pixels of dye from the donor element. When such a printer is used for making a color image, separate thermal dye colors (for example, cyan, magenta and yellow) are printed in sequence on the receiver element. It is advantageous to supply these colors on separate sheets or sections of donor film which are placed in succession against the receiver element onto which a color image is being printed. Thermal dye films suitable for this use are disclosed in U.S. Pat. No. 4,973,572, which has a common assignee with the present patent application.
From the standpoint of operating convenience and to obtain a more compact mechanism, it has been found to be desirable for the dye-donor film to be supplied in a thermal printer, such as disclosed in the above-identified patent application, as separate sheets packaged in a stack. Sheets of film are grouped in sets in a desired sequence of colors, and a convenient number of such sets are stacked together in a package. Because mishandling of and even minute amounts of contamination or dirt on the sheets of dye-donor film can cause visually objectionable spots and imperfections in a printed image, it is highly desirable that the film be kept in a clean and protected environment. The sheets of film should be delivered to the point of use in a thermal printer in an easily accessed package or cartridge with the film sheets properly grouped in sets in the individual sequences in which they will be used. The feeding of the individual sheets of film from the cartridge by the printer mechanism must be done with absolute reliability, but yet carefully, to avoid damage to the dye surface of the film. The present invention provides a highly effective yet inexpensive answer to these requirements for a dye-donor sheet film cartridge in a laser thermal printer.